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The light-second is a unit of length useful in astronomy, telecommunications and relativistic physics.It is defined as the distance that light travels in free space in one second, and is equal to exactly 299 792 458 m (approximately 983 571 055 ft or 186 282 miles).
The speed of light in IAU is the defined value c 0 = 299 792 458 m/s of the SI units. In terms of this speed, the old definition of the astronomical unit of length had the accepted value: [3] 1 au = c 0 τ A = (149 597 870 700 ± 3) m, where τ A is the transit time of light across the astronomical unit.
To do this, they redefined the metre as "the length of the path traveled by light in vacuum during a time interval of 1/ 299 792 458 of a second". [94] As a result of this definition, the value of the speed of light in vacuum is exactly 299 792 458 m/s [164] [165] and has become a defined constant in the SI system of units. [14]
The speed of light could then be expressed exactly as c 0 = 299 792 458 m/s, a standard also adopted by the IERS numerical standards. [19] From this definition and the 2009 IAU standard, the time for light to traverse an astronomical unit is found to be τ A = 499.004 783 8061 ± 0.000 000 01 s , which is slightly more than 8 minutes 19 seconds.
A value of 9.460 536 207 × 10 15 m found in some modern sources [15] [16] is the product of a mean Gregorian year (365.2425 days or 31 556 952 s) and the defined speed of light (299 792 458 m/s). Another value, 9.460 528 405 × 10 15 m, [17] is the product of the J1900.0 mean tropical year and the defined speed of light.
299 792 458 m⋅s −1: 0 [2] Planck constant: 6.626 070 15 × 10 −34 ...
= 299.792 458 V: volt (SI unit) V The difference in electric potential across two points along a conducting wire carrying one ampere of constant current when the power dissipated between the points equals one watt. [32] = 1 V = 1 W/A = 1 kg⋅m 2 /(A⋅s 3) = 1 J/C
"The metre is the length of the path travelled by light in vacuum during a time interval of 1 / 299 792 458 of a second." 17th CGPM (1983, Resolution 1, CR, 97) 1 / 10 000 000 of the distance from the Earth's equator to the North Pole measured on the circumference through Paris. L kilogram: kg mass